In general, a Radio Link Control (RLC) layer of a cellular network performs retransmission of a failed transmission of an RLC Protocol Data Unit (PDU) to provide reliable communication. For the retransmission of a failed transmission of an RLC PDU, an RLC entity of a receiving side (hereinafter referred to as a “reception RLC entity”) generates a status report recording a status including “success” or “failure” of reception of each of RLC PDUs received up to a current time from an RLC entity of a transmitting side (hereinafter referred to as a “transmission RLC entity”). Further, the reception RCL entity transmits the status report generated as described above to the transmission RLC entity. The generation of the status report may be largely divided into two types. In a first type, when the reception RLC entity detects reception failure of the RLC PDU, the reception RLC entity generates a status report by itself without a request of the transmission RLC and transmits the generated status report to the transmission RLC entity. In a second type, the transmission RLC entity explicitly transmits a request for the status report to the reception RLC entity. Thereafter, the reception RLC entity generates the status report and responds to the request.
Hereinafter, an RLC supporting a function of dividing one data stream into two or more radio access links, that is, Radio Access Technologies (RATs) and transmitting the divided RATs is defined as a multi-RAT RLC. In general, different radio access links have different transmission delay times by different characteristics of corresponding radio channels or different characteristics of protocols used in the radio channels. Accordingly, RLC PDUs transmitted through different radio access links by the multi-RAT RLC may experience different delay times. Hereinafter, such a delay is defined as an asymmetric transmission delay (hereinafter referred to as “skew”).
The receiving side receives a packet transmitted through a radio access link having a relatively short transmission delay time and, at a later time, receives a packet transmitted through a radio access link having a relatively long transmission delay time among packets almost simultaneously transmitted through a plurality of radio access links by the transmitting side. Accordingly, the receiving side receives out-of-order packets. Alternatively, a time point may exist when the receiving side receives the packet transmitted through the radio access link having the relatively short delay time but does not receive the packet transmitted through the radio access link having the relatively long delay time. In such a time point, in a point of view of a reception buffer of the RLC layer of the receiving side, the packet received through the radio access link having the relatively long delay time among packets which have not been received seems to be lost during the transmission.
In transmitting a status report to the transmission RLC entity, if the reception RLC entity transmits the status report without regard to the delay time generated due to a transmission delay time difference between different radio access links, a status report indicating transmission failure may be transmitted for packets which can be successfully received after a little delay time with a changed order. In this event, unnecessary retransmission by the transmitting side is made, and thus radio resources are wasted.
Therefore, a need exists for a method and an apparatus for transmitting a status report in a multi-RAT communication system supporting different RATs.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.